@Deddly Alright, thank you very much! I love the work you admins and moderators are doing. Great community.
Anyway, it would be lovely if you changed my username from "Roovy" to "DesertCookie", as this is the pseudonym I now use. Thank you very much!

Hey, I didn't know whether to create a new thread or use this one; but is it still you I have to ask if I want to change my username?
(I know it says at the bottom that this is an old thread and I should consider creating a new one, but just to do that for what I want to achieve seems like spaming to me...)

The KSP Fuel Calculator is a tiny tool to improve modders workflow. You can enter a fuel amount (lq. fuel or oxidizer) and the program calculates the missing propellant amount. You easily can do this by yourself with a calculator but this saves you some time if you are working on multiple fuel tanks or often have to chance it's values. The statistics may help you to not having to chance values for ballancing purposes too often. It currently just displays some vital informations about fuel cost and weight.
This tool isn't in active development any more! But please feel free to share ideas, I might have some time for it.
(watch out, outdated photos!)
Download: Alpha 0.3.1 (MEGA) Download: Alpha 0.3.1 (SpaceDock) Installation: Simply unzip the content of the downloaded file and place it where you need it. Create a shortcut if you want (.exe file for Windows, .jar file for Mac and Linux)
Source code: Alpha 0.3.1 (GitHub)
Version history:
Known issues:

The new version is here:
Release 0.2.4 brings some tiny bugfixes. The main feature is a way you now can calculate faster. Insert you numbers and just hit ENTER. It will automaticly trigger the 'Do calculation' button and... do the calculations?
Anyway, I'm looking towards your ideas.

The KSP Fuel Calculator is a tiny tool to improve modders workflow. You can enter a fuel amount (lq. fuel or oxidizer) and the program calculates the missing propellant amount. You easily can do this by yourself with a calculator but this saves you some time if you are working on multiple fuel tanks or often have to chance it's values. The statistics may help you to not having to chance values for ballancing purposes too often. It currently just displays some vital informations about fuel cost and weight.
Download: Alpha 0.2.5 (MEGA) Download: Alpha 0.3.3 (SpaceDock)
Source code: Alpha 0.3.3 (GitHub)
This tool is currently in developement. The alpha release gives me a chance to listen to your ideas on how to improve the design and functionality. I want to create a tool that makes modding easier and less time consuming. So please feel free to share any ideas you got.
Please look up the official thread fo more detailed information!

@Beetlecat @JeffreyCor @Nansuchao
Update 0.9 is out! The full version
I set down after a long while and thought about what I can do and came up with some tiny things:
I added KSP's internal fuelflow-system and removed the outdated crossfeedEnabler (since KSP 1.0.5) -> be shure to delete the old folder
I also made myself a plan on working out some minor things for release 1.0 (comming with KSP1.2). I will work a lot on the fuel amounts and weights. For example if the part is fueled they get heavier to keep stock ballance; also HRP's parts will get a litle less fuel capacity ('cause there must be some weak spot if they already are heat resistent!)
I'm looking toward your ideas. Maybe you can find some problems in the 1.2 pre-release that I can work on if they are appearing in KSP 1.2 final.
0.9 might be a tiny update, but since it's just the step from a beta to the release it is fine. Update 1.0 will be a bigger update tho and I'm not shure yet if a .1 jump in version is enough. I'm happy to be back and want to thank @NathanKell for his awesome mod CrossFeedEnabler that made a big part of this possible in the first place!

Update 0.9 (beta) is out!
Changes:
added optional version without InterstellarFuelSwitch
tiny changes to CrossFeedEnabler-cfg
cleaned up the installation folde
Version 0.9 (non-beta) will be released soon. Look up the download-sites for more informations.
@JeffreyCor I included your idea. Look up the Optional-folder and just install the non-InterstellarFuelSwitch version. (And delete the IStFs-folder

Update 0.75 is out! Here are the major changes:
reballance of already tweaked parts (yes, again!), also some changes to ISFs
tweaked total ballance of air-intakes (more at froum-thread)
added cross feed enabler
optional features added

Not exactly sure, but I think you have to use commas instead of "|". Didn't understood yet why the @ but I saw others use them like you did so wait for a second opinion.
But best way to figure this out is trying and learning from your mistakes...